For robotic joints with compliant transmissions, Mahvash and Okamura have proposed a friction compensator based on an elastoplastic friction model. One drawback of the compensator is that the compensator continues producing non-zero output force in the static friction state, which results in the degraded backdrivability of joints. In order to remedy this problem, this paper proposes an elastoplastic friction compensator with improved static friction behavior, which is realized by an additional term that makes the output force exponentially decay in the static friction state. This paper also proposes an additional algorithm that adjust the decay rate of the output force in real time. The proposed methods are experimentally tested with a linear actuator with a timing belt and a six-axis industrial manipulator.
2017 The Society of Instrument and Control Engineers